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Username Post: What Are My Options If I Don't Want Overdrive?        (Topic#354188)
Todd W. White 
Contributor
Posts: 287
Todd W. White
Loc: Sapulpa, Oklahoma
Reg: 02-08-08
12-03-18 06:41 AM - Post#2753159    

Hello All!

OK - I've determined that, with the configuration I have (engine, transmission, rear end ratio, tire size), that there isn't an overdrive transmission that will give me the ratio needed to work right in my truck. Plus, the cost to do the swap wouldn't ever pay for itself in gas savings.

SO -

I am using an SM420, and I like it, BUT, even fully rebuilt, they "whine" at highway speeds, making conversation difficult. And the whine is annoying. Not only that, but the SM420 is SLOW to take off from a dead stop, and I'm tired of people behind me getting annoyed at me because they want to "get going" faster than I can reasonably do with the SM420.

I would like to know what you fellows suggest I switch to. Ideally, I would like something that bolts right up to my current bell housing and uses the same clutch and has a floor shifter, because I have a high hump floor. An alternative would be swapping out to a low hump, if possible, and using a column shifter. I suppose I could even switch to an automatic, although I am leery of that because of long-term availability of parts.

What do you guys recommend?



 

Ecklers AutoMotive

raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-03-18 08:52 PM - Post#2753281    
    In response to Todd W. White

I replaced my SM420 with a T-5 because I wanted taller gearing and the T-5 was less work and money than a different rear end, which would have also required some welding because my truck is a 60. I kept my original bellhousing and had to replace only the clutch disc to match the input spline on the T-5. Also, the T-5 has closer ratios and can be shifted much faster than the SM420, which made a noticeable improvement in the truck's acceleration.

Regarding your noise, I can say with absolute certainty that a SM420 in good condition does not make any noise in 4th gear. Have you considered the possibility that your whine might be coming from the rear axle instead of the trans? Also, what year and model is your truck?

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Woogeroo 
Valued Contributor
Posts: 2787
Woogeroo
Loc: what does this part do?
Reg: 05-26-02
12-04-18 03:45 AM - Post#2753297    
    In response to raycow

If you are interested in the T5, go to this blog and check out the T5 info page :

Lugnutz65ChevyStepside



 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-04-18 02:46 PM - Post#2753367    
    In response to Woogeroo

That is a very helpful site, and the text is well supported with excellent photographs. Thank you for posting the link.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
sidworks 
Valued Contributor
Posts: 3507

Age: 73
Loc: Sidney, B.C.
Reg: 12-03-05
12-07-18 12:51 PM - Post#2753758    
    In response to raycow

  • raycow Said:
I replaced my SM420 with a T-5 because I wanted taller gearing and the T-5 was less work and money than a different rear end, which would have also required some welding because my truck is a 60. I kept my original bellhousing and had to replace only the clutch disc to match the input spline on the T-5. Also, the T-5 has closer ratios and can be shifted much faster than the SM420, which made a noticeable improvement in the truck's acceleration.

Regarding your noise, I can say with absolute certainty that a SM420 in good condition does not make any noise in 4th gear. Have you considered the possibility that your whine might be coming from the rear axle instead of the trans? Also, what year and model is your truck?

Ray



Ray: he has a 3:08 rear end so he doesn't really need an od trans unless he has a more torqueful engine to push it in OD.. he best application would be to get a car 4 speed; rebuild it and put it in and drive it. this would give him the
first gear that he desires and a closer ratio. it will bolt up to his b/housing,have a floor shift, will not have to put in a rear trans xmember, but more than likely have to refit the front of his d/shaft. 4th will be direct but he has the 3:08s in the back so that will give him the same results as he is getting with the truck 4 speed which he has in there now. if he uses a bw t10 he may get away without changing the d/shaft but am not sure about that.
ron

http://www.sawmillcreek.org/showthread.php?208929-...
http://www.sawmillcreek.org/showthread.php?220902-...
http://forum.woodenboat.com/showthread.php?156542-...


 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-08-18 05:55 AM - Post#2753835    
    In response to sidworks

Ron, I agree that with a 3.08 the OP probably doesn't need OD. Also, a car 4 speed would be a good choice for improving acceleration. At least it would be a lot faster to shift than the SM420.

As for the driveshaft, there isn't much hope of modifying the old one. The SM420 output has a bolted yoke so its driveshaft has a slip joint built in. A car 4 speed would need a conventional type of shaft with a slip yoke at the front. When I installed my T-5 I found a salvage yard shaft with the correct U-joints and spline and had it shortened a bit.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Todd W. White 
Contributor
Posts: 287
Todd W. White
Loc: Sapulpa, Oklahoma
Reg: 02-08-08
12-08-18 09:07 AM - Post#2753859    
    In response to raycow

Thanks guys! The car transmission sounds like a good idea. Three questions:

1. Would it have enough strength to pull a trailer like I sometimes do?

2. Would the gearshift be on the floor or on the column? (which kind of depends, I suppose, on the answer to #3)

3. What would you suggest as good candidates to look for?

THANKS AGAIN!



 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-08-18 01:25 PM - Post#2753893    
    In response to Todd W. White

I didn't realize you were towing with your rig. That does make a difference. The issue isn't trans strength, but rather 1st gear ratio. The lowest 1st gear you can get with a car 4 speed is about 3.50, which is roughly the same as 2nd gear on the SM420.

So the big question is, do you find yourself needing 1st gear on the SM420? If yes, then you will likely have to stay with a truck trans, either 4 or 5 speed.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Todd W. White 
Contributor
Posts: 287
Todd W. White
Loc: Sapulpa, Oklahoma
Reg: 02-08-08
12-08-18 02:48 PM - Post#2753899    
    In response to raycow

Not really. Only on rare occasions do I need the granny gear. I usually use 2nd as 1st.



Edited by Todd W. White on 12-08-18 03:33 PM. Reason for edit: No reason given.

 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-08-18 04:09 PM - Post#2753907    
    In response to Todd W. White

Ok, then you should be good to go with a car 4 speed. However, be sure to check the 1st gear ratio on your selection before you lay down your money.

Here is a list of ratios available for Super T-10:
https://www.chevelles.com/forums/40-2004/23335- sup...

Muncie ratios here:
http://www.5speeds.com/muncie/home/new-trans missio...

Saginaw possibilities here:
http://nastyz28.com/threads/saginaw-4-spe ed-gear-r...

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Todd W. White 
Contributor
Posts: 287
Todd W. White
Loc: Sapulpa, Oklahoma
Reg: 02-08-08
12-08-18 07:27 PM - Post#2753929    
    In response to raycow

Great!

So - should I look for a transmission from a car of the same era (mid-60s), which cars, and which transmissions have floor shifters that would be compatible with my high hump floor and still clear the bench seat?

Sorry for all the questions...



 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-09-18 01:32 AM - Post#2753952    
    In response to Todd W. White

Sorry, but I can't offer any help with particular makes and years. If you want to use the OE shifter, my best advice would be to take a tape measure with you when you go shopping. Measure from the bellhousing face to the shifter. Hurst makes aftermarket bench seat shifters for quite a few transmissions, but that would be a considerable extra expense.

I don't think the high hump should cause a problem. However, don't expect to use the existing hole in the hump. The car shifter will be left of center, so you will likely have to do some cutting and patching. My T-5 shifter is centered because it has internal linkage, but it still comes through several inches to the rear of the SM420 hole. It didn't have any seat clearance issues though.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Todd W. White 
Contributor
Posts: 287
Todd W. White
Loc: Sapulpa, Oklahoma
Reg: 02-08-08
12-10-18 01:08 PM - Post#2754086    
    In response to raycow

I wonder - can the high hump be replaced with a low hump, and then a hole cut in the low hump to match whichever car transmission I end up with?



 
raycow 
Honored Member
Posts: 27994
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-10-18 05:19 PM - Post#2754108    
    In response to Todd W. White

I will gladly stand corrected on this, but I THINK the low hump is welded in.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 

Ecklers AutoMotive

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